Electromagnetic tracking surgical system and method of controlling the same

ABSTRACT

An electromagnetic (EM) system for tracking a surgical tool is provided. The system may comprise a plurality of subsets of field generator coils disposed along edge portions of a surgical bed. Each subset of field generator coils may be configured to generate a magnetic field within a control volume. The system may further comprise a position sensor disposed on a portion of the surgical tool. The position sensor may be configured to generate a sensor signal in response to the magnetic field when the position sensor is located inside the control volume. Additionally, the system may comprise an EM system controller configured to selectively activate one or more of the subsets of field generator coils based on the sensor signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/278,925 entitled “Electromagnetic TrackingSurgical System and Method of Controlling the Same,” filed Jan. 14,2016, the disclosure of which is hereby incorporated by reference in itsentirety.

BACKGROUND 1. Field of the Invention

The field of the present application pertains to medical devices. Moreparticularly, the field of the invention pertains to an electromagnetictracking surgical system and a method of controlling the same.

2. Description of the Related Art

A surgical procedure may be performed on a patient using one or moresurgical tools when the patient is placed on a surgical bed. Thesurgical tools may include endoscopes, catheters, ureteroscopes, orother similar devices. Endoscopy is a widely-used, minimally invasivetechnique for both imaging and delivering therapeutics to anatomicallocations within the human body. Typically a flexible endoscope is usedto deliver tools to an operative site inside the body—e.g., throughsmall incisions or a natural orifice in the body—where a surgicalprocedure is to be performed. Endoscopes may have imaging, lighting, andsteering capabilities at the distal end of a flexible shaft enablingnavigation of non-linear lumens or pathways.

SUMMARY

In one aspect of the invention, an electromagnetic (EM) system fortracking a surgical tool is provided. A sensor associated with asurgical tool may be tracked based on interactions of the sensor with anelectromagnetic field. In particular, a sensor associated with asurgical tool may be tracked when voltage is induced within a sensorcoil that is placed within the electromagnetic field. In examples, thesystem provided may be used for alternating current (AC) EM tracking. Inother examples, the system may be used for direct current (DC) EMtracking.

The electromagnetic field may be calibrated having a predeterminedprecision along a length of a surgical bed in the system. Smallvariations in position of the surgical device can be detected based onthe sensor interaction with the electromagnetic field. The positionalvariations can have a spatial resolution of less than about 10 mm, 9 mm,8 mm, 7 mm, 6 mm, 5 mm, 4 mm, 3 mm, 2 mm, 1 mm, or less than 1 mm. Insome cases, the spatial resolution may be greater than about 10 mm.

The system may comprise a plurality of subsets of field generator coilsdisposed along edge portions of a surgical bed. Each subset of fieldgenerator coils may be configured to generate a magnetic field within acontrol volume. In some examples, the control volume may be static. Insome examples, the control volume may be capable of changing dynamically(for example, but not limited to, time-variable). The system may furthercomprise a position sensor disposed on a portion of the surgical tool.The position sensor may be configured to generate a sensor signal inresponse to the magnetic field when the position sensor is locatedinside the control volume. Additionally, the system may comprise an EMsystem controller configured to selectively activate one or more of thesubsets of field generator coils based on the sensor signal. Inexamples, a system may comprise more than one position sensor. In someexamples, more than one position sensor may be capable of interactingwith an electromagnetic field. In additional examples, one or moreposition sensors on a surgical tool having multiple position sensors maybe activated at a time. In further examples, one or more positionsensors on a surgical tool having multiple position sensors may beselectively activated. In some modes, multiple position sensors may beactivated simultaneously. In some modes, position sensors may beactivated one at a time. Additionally, an EM tracking surgical systemmay be capable of working in more than one mode. In these examples, asurgical system may switch between modes.

In some cases, a physician may need to know the spatial information ofan endoscope relative to the patient's body, using the surgical bed as adatum. The spatial information may include a spatial position and/ororientation of the endoscope in a three-dimensional coordinate system.In some examples, spatial information received regarding an endoscopemay be corroborated by additional sensor-based information. Inparticular, information regarding a spatial location of a sensor basedon the sensor's interaction with an EM field may be corroborated byimaging information that is received from an imaging sensor, e.g., froma camera that is located on or near the surgical tool. One or moresensors may be attached to the endoscope to determine the spatialinformation. The sensors may include electromagnetic (EM) sensorsconfigured to detect the spatial information of the endoscope, as wellas movement of the endoscope, within the environment of the surgicalbed. The EM sensors may be used in conjunction with a set of fieldgenerator coils that are disposed at or proximal to the surgical bed.The field generator coils may be configured to produce a calibrated (forexample, but not limited to, known) electromagnetic (EM) field over aworking volume proximal to the surgical bed. The working volume may bedefined as a three-dimensional space above the surgical bed where aportion of the patient's body is located. A region of interest on thepatient's body (for example, but not limited to, where a surgicalprocedure is to be performed) may be disposed within the working volume.When the endoscope moves within the working volume, the interaction ofthe EM sensors with the EM field results in electrical signals (forexample, but not limited to, voltages) being generated. The spatialinformation and/or movement of the endoscope can be determined byanalyzing the electrical signals.

Current state-of-the-art field generator coils may be provided indifferent configurations. For example, in some cases, a flatconfiguration of field generator coils may be placed in a surgical beddirectly under a patient. Alternatively, a box configuration ofgenerator coils may be placed externally on a side of the surgical bedor positioned above/over the patient. Optionally, a window configurationof generator coils may be positioned under the surgical bed or under thepatient. However, each of the above configurations has certaindeficiencies. For example, use of fluoroscopy may be limited in the flatconfiguration because the generator coils constitute radio-opaqueobjects/regions that can obstruct fluoroscopic imaging (for example, butnot limited to, X-ray imaging). The box configuration may interfere witha physician's access to a patient since the coils are placed externallyon the side of the surgical bed or positioned above/over the patient. Inthe window configuration, the positioning of coils under the surgicalbed may result in mechanical and/or electromagnetic interference withother devices (for example, but not limited to, motors for actuating thebed, linear actuator drives, radio-frequency (RF) circuits, etc.) thatare also disposed under the surgical bed. Additionally, the positioningof coils under the patient may require an overall thickness of the bedto be increased, which may result in larger form factor and highermanufacturing costs.

Additional drawbacks of one or more of the above coil configurations mayinclude limited range of use. For example, the field generators in theabove configurations typically generate a working volume of about 0.5m×0.5 m×0.5 m, which is often insufficient to encompass a length or awidth of a patient's body. In some instances, the surgical procedure mayinvolve different parts of the patient's body that are spaced outside ofthe typical 0.5 m×0.5 m×0.5 m working volume. In those instances,movement of the coils around the surgical bed may be required, which mayincrease the mechanical complexity of the system and interfere with thephysician's access to the patient.

Accordingly, it would be beneficial to have an integrated EM trackingsurgical system and a method of controlling the system that provideimproved navigation, ergonomics, and usability.

An electromagnetic (EM) system for tracking a surgical tool may beprovided in accordance with another aspect of the invention. The systemmay comprise a plurality of subsets of field generator coils disposedalong edge portions of a surgical bed. Each subset of field generatorcoils may be configured to generate a magnetic field within a controlvolume. A central portion of the surgical bed may be fluoroscopicallytransparent. The system may also comprise a position sensor disposed ona portion of the surgical tool. The position sensor may be configured togenerate a sensor signal in response to the magnetic field when theposition sensor is located inside the control volume. The system mayfurther comprise an EM system controller configured to activate one ormore of the subsets of field generator coils.

It shall be understood that different aspects of the invention can beappreciated individually, collectively, or in combination with eachother. Other objects and features of the present invention will becomeapparent by a review of the specification, claims, and appended figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described, by way of example, and with referenceto the accompanying drawings, in which:

FIG. 1 illustrates a schematic of an electromagnetic (EM) trackingsurgical system, in accordance with some embodiments;

FIG. 2 illustrates a block diagram of a closed-loop control EM trackingsurgical system, in accordance with some embodiments;

FIG. 3 illustrates a schematic circuit diagram of an EM trackingsurgical system, in accordance with some embodiments;

FIG. 4 illustrates schematic layouts of the field generator coils andworking volumes within an EM tracking surgical system, in accordancewith some embodiments;

FIG. 5 illustrates selective activation of field generator coils andworking volumes as a surgical tool comprising a position sensor thatmoves within an EM tracking surgical system, in accordance with someembodiments;

FIG. 6 illustrates selective activation of field generator coils andworking volumes as a surgical tool comprising a plurality of positionsensors that move within an EM tracking surgical system, in accordancewith some embodiments;

FIG. 7 illustrates schematic views of an EM tracking surgical systemhaving reconfigurable bed portions, in accordance with some embodiments;

FIG. 8 illustrates a perspective view of an EM tracking surgical systemhaving a reconfigurable bed portion, in accordance with someembodiments;

FIGS. 9A and 9B illustrate sizing of a reconfigurable bed portion of anEM tracking surgical system based on exemplary dimensions of a humantorso, in accordance with some embodiments;

FIG. 10 illustrates a reconfigurable bed portion of an EM trackingsurgical system, in accordance with some embodiments;

FIG. 11 illustrates dimensions and locations of field generator coils ona reconfigurable bed portion of an EM tracking surgical system, inaccordance with some embodiments;

FIG. 12 illustrates an estimated length of a working volume based on thedimensions of a reconfigurable bed portion of an EM tracking surgicalsystem, in accordance with some embodiments; and

FIG. 13 illustrates an exemplary working volume above a reconfigurablebed portion of an EM tracking surgical system, in accordance with someembodiments.

DETAILED DESCRIPTION

Although certain preferred embodiments and examples are disclosed below,the inventive subject matter extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses, and tomodifications and equivalents thereof. Thus, the scope of the claimsappended hereto is not limited by any of the particular embodimentsdescribed below. For example, in any method or process disclosed herein,the acts or operations of the method or process may be performed in anysuitable sequence and are not necessarily limited to any particulardisclosed sequence. Various operations may be described as multiplediscrete operations in turn, in a manner that may be helpful inunderstanding certain embodiments; however, the order of descriptionshould not be construed to imply that these operations are orderdependent. Additionally, the structures, systems, and/or devicesdescribed herein may be embodied as integrated components or as separatecomponents.

For purposes of comparing various embodiments, certain aspects andadvantages of these embodiments are described. Not necessarily all suchaspects or advantages are achieved by any particular embodiment. Thus,for example, various embodiments may be carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other aspects or advantages as mayalso be taught or suggested herein.

1. Overview

An electromagnetic (EM) tracking surgical system may be provided inwhich field generator coils are embedded along edge portions of asurgical bed. The placement of field generator coils in the disclosedconfigurations allows for unobstructed use of fluoroscopic imaging, andallows a physician to easily access the patient during a surgicalprocedure. Unlike some conventional systems, the field generator coilsin the disclosed EM tracking surgical systems do not interfere with thephysician's access to the patient. The integration of the fieldgenerator coils along the edge portions of the surgical bed also allowsthe surgical bed to remain compact since it does not increase theoverall thickness of the surgical bed.

The disclosed configurations of field generator coils also allow aplurality of EM fields to be selectively activated within differentworking volumes above the surgical bed. The selective activation of EMfields within the different working volumes can prevent interfering EMfields from being generated, and can reduce EM interference between thefield generator coils and other devices. Reduction in EM interferencecan improve the accuracy and sensitivity with which a surgical tool (forexample, but not limited to, an endoscope having one or more EM sensors)can be tracked within the different working volumes above the surgicalbed. Additionally, the disclosed configurations of field generator coilscan extend the range of use of the system by a physician, since theworking volumes can be configured to extend along a length of thesurgical bed or in other configurations, depending on the requirementsand complexity of the surgical procedure.

Tracking of a surgical tool can be facilitated by activating differentsubsets of field generator coils. In examples, different subsets offield generator coils may be activated depending on the location of thesurgical procedure relative to the surgical bed. In some examples, as asurgical procedure progresses to different areas of a patient, fieldgenerator coils associated with different portions of the bed may beactivated. Additionally, in examples, coils outside of the activesubset(s) of field generator coils are inactive, thereby preventinginterfering EM fields from being generated. In some examples, theworking volumes above adjacent subsets of field generator coils mayoverlap so as to form a continuous global working volume along thelength of the surgical bed.

2. System Components

FIG. 1 illustrates a schematic of an EM tracking surgical system, inaccordance with some embodiments. As shown in FIG. 1, EM trackingsurgical system 100 may comprise a surgical bed 102, a plurality offield generator coils 103, an EM system controller 108, a switch module110, a plurality of working volumes 112, and a position sensor 116.

The surgical bed 102 may be configured to support a patient. A physicianmay perform a surgical procedure on the patient while the patient isplaced on the surgical bed 102. In some embodiments, the surgical bed102 may comprise multiple sections that are movable relative to oneanother. In those embodiments, the patient's body can be moved intodifferent positions by moving different sections of the surgical bed 102relative to one another. Alternatively, the surgical bed 102 may beformed monolithically as a single rigid structure.

The plurality of field generator coils 103 may be embedded or integratedalong edge portions of the surgical bed 102. For example, as shown inFIG. 1, the plurality of field generator coils 103 may be embedded alonga length of the surgical bed 102 in two rows 106. The rows 106 mayextend parallel to each other along the edge of the surgical bed 102. Aspreviously mentioned, the field generator coils 103 constituteradio-opaque objects/regions. Accordingly, the placement of the fieldgenerator coils 103 along the edges of the surgical bed 102 can allowunobstructed use of fluoroscopy to image the patient's body during asurgical procedure.

In some examples, the plurality of field generator coils 103 may bewithin one group of field generator coils that are associated with aworking volume 112. The plurality of field generator coils 103 mayinclude, and can be grouped into, subsets as field generator coils 104.For example, as shown in FIG. 1, the field generator coils 103 mayinclude a first subset of field generator coils 104-1, a second subsetof field generator coils 104-2, and a third subset of field generatorcoils 104-3. Although three subsets are illustrated in FIG. 1, it shouldbe noted that the invention is not limited thereto, and that any numberof subsets of field generator coils may be contemplated. In examples,field generator coils 103 may be grouped into 2, 3, 4, 5, 6, 7, 8, 9,10, or more than 10 subsets.

Each subset of field generator coils 104 may comprise a number of fieldgenerator coils. In FIG. 1, each subset of field generator coils 104-1,104-2, and 104-3 may comprise eight field generator coils. However, eachsubset of field generator coils need not be limited to eight fieldgenerator coils. In some embodiments, a subset of field generator coilsmay comprise more than eight field generator coils. For example, asubset of field generator coils may comprise 9, 10, 11, 12, 13, 14, 15,16, 17, 18, 19, 20, 25, 30, 35, 40, or more than 40 field generatorcoils. In other embodiments, a subset of field generator coils maycomprise less than eight field generator coils. For examples, a subsetof field generator coils may comprise 1, 2, 3, 4, 5, 6, or 7 fieldgenerator coils. In some embodiments, different subsets of fieldgenerator coils may comprise different numbers of field generator coils.Any number of field generator coils within each subset, and betweendifferent subsets, may be contemplated.

The field generator coils within each subset may be fixed in placerelative to one another. For example, the field generator coils may bespaced apart by a predetermined distance and/or at a predefined pitchalong the edges of the surgical bed 102. Additionally, the subsets offield generator coils may be nominally fixed relative to the surgicalbed 102 in a global coordinate system. Any portion of the surgical bed102 may serve as an origin of the global coordinate system. In someembodiments, a datum point that lies substantially above a centerportion of the surgical bed 102 may serve as the origin of the globalcoordinate system. In those embodiments, the positions of the subsets offield generator coils may be defined relative to the datum point.

In some embodiments, when the surgical bed comprises multiple sectionsthat are movable relative to one another, the subsets of field generatorcoils may not be fixed in position relative to one another. Instead, thesubsets of field generator coils may be located on one or more movablesections, and can move relative to one another when one or more sectionsof the surgical bed move. In those embodiments, global tracking of asurgical tool can be facilitated by adding sensors to the surgical bedthat can detect changes in the configuration of the surgical bed.

As shown in FIG. 1, the plurality of working volumes 112 may include afirst working volume 112-1, a second working volume 112-2, and a thirdworking volume 112-3. Each working volume 112 may be associated with asubset of field generator coils, and may be disposed directly above therespective subset of field generator coils. For example, the firstworking volume 112-1 may be disposed directly above the first subset offield generator coils 104-1, the second working volume 112-2 may bedisposed directly above the second subset of field generator coils104-2, and the third working volume 112-3 may be disposed directly abovethe third subset of field generator coils 104-3.

In some embodiments, adjacent working volumes 112 may overlap each otherto form an overlapping working volume 114. As shown in FIG. 1, a firstoverlapping working volume 114-1 may be formed by an overlapping regionbetween the first working volume 112-1 and the second working volume112-2. Similarly, a second overlapping working volume 114-2 may beformed by an overlapping region between the second working volume 112-2and the third working volume 112-3. A size and/or shape of theoverlapping working volumes 112 (i.e., the amount of overlap betweenadjacent working volumes) can be modified by adjusting the locations ofthe subsets of field generator coils. The size and/or shape of theoverlapping working volumes can depend on the tolerance, sensitivity,position, and/or orientation of the field generator coils. The sizeand/or shape of the overlapping working volumes may be adjusted tooptimize the magnetic flux uniformity therein, which can help to improveaccuracy of the EM tracking. The overlapping working volumes may besymmetrical or non-symmetrical. The overlapping working volumes can haveregular shapes or irregular shapes. Examples of regular shapes mayinclude elliptical, cylindrical, or cubic shapes. In some alternativeembodiments, the plurality of working volumes need not overlap. Forexample, adjacent subsets of field generator coils may be pulsed (forexample, but not limited to, activated) sequentially such that theworking volumes do not overlap. Alternatively, adjacent subsets of fieldgenerator coils may be orientated in a configuration that does notcreate overlapping working volumes. For example, adjacent subsets offield generator coils may not be disposed parallel to one another.Additionally, the working volumes may not overlap if adjacent subsets offield generator coils are spaced apart by at least a predefineddistance. The predefined distance may be 1 m, 1.1 m, 1.2 m, 1.3 m, 1.4m, 1.5 m, or greater than 1.5 m. Alternatively, the predefined distancemay be less than 1 m. It should be noted that the amount of overlapbetween adjacent working volumes can affect the tracking performance ofthe system. For example, a large amount of overlap can providecontinuously-joined working volumes, and ensure that the sensor can betracked as it moves from one control volume to the next. However, alarge amount of overlap may generate in-frequency noise which can impedetracking performance. Conversely, a small amount of overlap (or nooverlap) can reduce in-frequency noise, but there is a risk of thesystem momentarily losing track of the sensor position as the sensormoves between control volumes.

The EM system controller 108 may be configured to provide electricalcurrent pulses to the field generator coils 103 to generate an EM fieldover the respective working volume 112 above each subset of fieldgenerator coils 104. The EM system controller 108 can selectivelyactivate (for example, but not limited to, power on) different subsetsof field generator coils 104 to generate EM fields in different workingvolumes 112 by controlling one or more switches in the switch module110. Electrical current pulses may be provided from the EM systemcontroller 108 to the different subsets of field generator coils 104 viaone or more switches in the switch module 110.

The switches may include electronic switches such as power MOSFETs,solid state relays, power transistors, and/or insulated gate bipolartransistors (IGBTs). Different types of electronic switches may beprovided for controlling current to a subset of field generator coils.An electronic switch may utilize solid state electronics to controlcurrent flow. In some instances, an electronic switch may have no movingparts and/or may not utilize an electro-mechanical device (for example,but not limited to, traditional relays or switches with moving parts).In some instances, electrons or other charge carriers of the electronicswitch may be confined to a solid state device. The electronic switchmay optionally have a binary state (for example, but not limited to,switched-on or switched-off). The electronic switches may be used tocontrol current flow to the subsets of field generator coils. Theoperation of switches to selectively activate one or more subsets offield generator coils 104 is described with reference to FIG. 3, below.

The EM system controller 108 can control the switches to activate: (1)the first subset of field generator coils 104-1 to generate an EM fieldin the first working volume 112-1, (2) the second subset of fieldgenerator coils 104-2 to generate an EM field in the second workingvolume 112-2, and/or (3) the third subset of field generator coils 104-3to generate an EM field in the third working volume 112-3. In examples,the subsets of field generator coils may be activated simultaneously. Insome examples, the subsets of field generator coils may be activatedsequentially. For example, in some embodiments, the EM system controller108 can simultaneously activate all three subsets of field generatorcoils 104 to create three separate EM fields in the respective workingvolumes 112. Alternatively, the EM system controller 108 cansequentially activate the first, second, and third subsets of fieldgenerator coils 104-1, 104-2, and 104-3 to sequentially generate EMfields in the first, second, and third working volumes 112-1, 112-2, and112-3.

The EM system controller 108 can be configured to activate one or moresubsets of field generator coils without activating one or more othersubsets of field generator coils. For example, in some embodiments, theEM system controller 108 can activate only the first subset of fieldgenerator coils 104-1 without activating the second and third subsets offield generator coils 104-2 and 104-3. Similarly, the EM systemcontroller 108 can activate only the second subset of field generatorcoils 104-2 without activating the first and third subsets of fieldgenerator coils 104-1 and 104-3. Likewise, the EM system controller 108can activate only the third subset of field generator coils 104-3without activating the first and second subsets of field generator coils104-1 and 104-2. In some cases, the EM system controller 108 canactivate the first and second subsets of field generator coils 104-1 and104-2 without activating the third subset of field generator coils104-3. In other cases, the EM system controller 108 can activate thesecond and third subsets of field generator coils 104-2 and 104-3without activating the first subset of field generator coils 104-1.Optionally, the EM system controller 108 can activate the first andthird subsets of field generator coils 104-1 and 104-3 withoutactivating the second subset of field generator coils 104-2. Additionalcombinations (for example, but not limited to, of the activation) ofdifferent subsets of field generator coils may be contemplated.

As previously described, the EM system controller 108 can sequentiallyactivate the first, second, and third subsets of field generator coils104-1, 104-2, and 104-3. In some embodiments, all three subsets of fieldgenerator coils may continue to be powered on after they have beensequentially activated. For example, the first subset of field generatorcoils 104-1 may continue to be powered on after the second subset offield generator coils 104-2 has been activated. The first and secondsubsets of field generator coils 104-1 and 104-2 may continue to bepowered on after the third subset of field generator coils 104-3 hasbeen activated. Alternatively, in some embodiments, the first subset offield generator coils 104-1 may be powered off after the second subsetof field generator coils 104-2 has been activated, and the second subsetof field generator coils 104-2 may be powered off after the third subsetof field generator coils 104-3 has been activated.

In some embodiments, the EM system controller 108 may be located on thesurgical bed 102, for example on a base configured to support thesurgical bed 102. In some embodiments, the EM system controller 108 maybe located remotely from the surgical bed 102. For example, the EMsystem controller 108 may be disposed in a remote server that is incommunication with the subsets of field generator coils 104 and theswitch module 110. The EM system controller 108 may be software and/orhardware components included with the server. The server can have one ormore processors and at least one memory for storing programinstructions. The processor(s) can be a single or multiplemicroprocessors, field programmable gate arrays (FPGAs), or digitalsignal processors (DSPs) capable of executing particular sets ofinstructions. Computer-readable instructions can be stored on a tangiblenon-transitory computer-readable medium, such as a flexible disk, a harddisk, a CD-ROM (compact disk-read only memory), and MO(magneto-optical), a DVD-ROM (digital versatile disk-read only memory),a DVD RAM (digital versatile disk-random access memory), or asemiconductor memory. Alternatively, the program instructions can beimplemented in hardware components or combinations of hardware andsoftware such as, for example, ASICs, special purpose computers, orgeneral purpose computers.

The EM system controller 108 may also be provided at any other type ofexternal device (for example, but not limited to, a remote controllerfor controlling the surgical bed 102 and/or a surgical tool, any movableobject or non-movable object, etc.). In some instances, the EM systemcontroller 108 may be distributed on a cloud computing infrastructure.The EM system controller 108 may reside in different locations where theEM system controller 108 is capable of controlling the switch module 110and selectively activating one or more subsets of field generator coils104 based on the spatial information of the position sensor 116.

The position sensor 116 may be disposed in or on a portion of a surgicaltool. For example, in some embodiments, the position sensor 116 may bedisposed at a distal end of the surgical tool. Examples of surgicaltools may include endoscopes, catheters, ureteroscopes, forceps,different types of scopes, or other similar devices or surgicalaccessories.

A position sensor, such as position sensor 116, may be configured togenerate an electrical signal (for example, but not limited to, voltageor current signal) in response to EM fields generated by one or moresubsets of field generator coils 104. Position sensor 116 may be an EMsensor. As position sensor 116 moves within a control volume 112, theinteraction of the position sensor 116 with the EM field within thecontrol volume 112 may cause electrical signals to be generated. Theelectrical signals may vary as the position sensor 116 moves betweendifferent locations within a control volume 112. Additionally,electrical signals may vary as the position sensor 116 moves betweendifferent control volumes. The EM system controller 108 may beconfigured to receive electrical signals from the position sensor 116.Additionally, the EM system controller 108 may analyze the signals tocompute a local position of the sensor 116. The local position of thesensor 116 may be computed relative to a local coordinate system. Thelocal coordinate system may be defined at an active subset of fieldgenerator coils 104 corresponding to the control volume 112 in which theposition sensor 116 is located.

The EM system controller 108 may be further configured to compute aglobal position of the sensor 116 relative to a global coordinatesystem. The global coordinate system may be defined at the surgical bed102 (for example, but not limited to, above a center portion of thesurgical bed 102). The global position of the sensor 116 may be computedbased on: (1) the local position of the sensor 116 within the controlvolume 112 above an active subset of field generator coils 104, and (2)the position of the active subset of field generator coils 104 relativeto the surgical bed 102. The global position of the sensor 116 may beused to determine a position of a surgical tool relative to a patient onthe surgical bed 102.

The EM system controller 108 may be configured to control the switchmodule 110 based on one or more inputs. The control of the switch module110, and the selective activation of one or more subsets of fieldgenerator coils 104, may be manual and/or automatic.

In some embodiments, the EM system controller 108 may control the switchmodule 110 based on a user input corresponding to a selection of aregion (or working volume 112) of the surgical bed 102 where tracking ofa surgical tool is desired. For example, a physician may plan to performa surgical procedure on a patient in a region within the first workingvolume 112-1. Accordingly, the physician or the physician's assistantmay provide an input to the EM system controller 108 to activate thefirst subset of field generator coils 104-1, so that movement of thesurgical tool can be tracked within the first control volume via theposition sensor 116.

In some embodiments, the EM system controller 108 may control the switchmodule 110 based on an input indicative of the sensor position and/ormovement within a control volume 112 above an active subset of fieldgenerator coils 104. For example, when the EM system controller 108detects that the position sensor 116 is inside the first working volume112-1 but outside of the first overlapping working volume 114-1, the EMsystem controller 108 may control the switch module 110 to activate onlythe first subset of field generator coils 104-1.

In some embodiments, when the EM system controller 108 detects that theposition sensor 116 has moved into an overlapping working volume 114between adjacent working volumes 112, the EM system controller 108 maycontrol the switch module 110 to activate the subsets of field generatorcoils 104 corresponding to both working volumes 112 that have a portionwithin the overlapping working volume 114, so as to ensure that theposition sensor 116 can continue to be tracked in the overlappingworking volume 114 (for example, but not limited to, where the EM fieldstrength may be lower). For example, when the EM system controller 108detects that the position sensor 116 has moved into the firstoverlapping working volume 114-1, the EM system controller 108 maycontrol the switch module 110 to activate both the first and secondsubsets of field generator coils 104-1 and 104-2 associated with workingvolumes 112-1 and 112-2, to ensure that the position sensor 116 cancontinue to be tracked in the first overlapping working volume 114-1.

In some embodiments, when the EM system controller 108 detects that theposition sensor 116 has moved into the first overlapping working volume114-1 and is moving from the first working volume 112-1 towards thesecond working volume 112-2, the EM system controller 108 may controlthe switch module 110 to activate both the first and second subsets offield generator coils 104-1 and 104-2 associated with working volumes112-1 and 112-2, so as to ensure a smooth EM field transition (and insome examples but not limited to, continuous tracking/sensing) as theposition sensor 116 moves between the first and second working volumes112-1 and 112-2.

In some embodiments, when the EM system controller 108 detects that theposition sensor 116 has moved into the second working volume 112-2 butoutside of the first overlapping working volume 114-1, the EM systemcontroller 108 may control the switch module 110 to activate the secondsubset of field generator coils 104-2 and power off the first subset offield generator coils 104-1. By selectively activating the subsets offield generator coils 104 based on the position and/or movement of theposition sensor 116, interference between adjacent EM fields can bereduced or mitigated. Additionally, the energy needed to power the fieldgenerator coils 104 can be reduced, since not all of the field generatorcoils have to be powered on at the same time.

In some embodiments, the EM system controller 108 may control the switchmodule 110 based on an initialization input. The initialization inputmay cause the EM system controller 108 to control the switch module 110to sequentially activate (for example, but not limited to, cyclethrough) the subsets of field generator coils 104, so as to determine:(1) whether the position sensor 116 is present in any of the controlvolumes 112, (2) in which control volume 112 the position sensor 116 islocated if the position sensor 116 is detected, and (3) the position ofthe sensor 116 within the detected control volume 112. Accordingly, theEM system controller 108 can control the switch module 110 to activatethe subset of field generator coils 104 corresponding to the controlvolume 112 in which the position sensor 116 is located, withoutactivating the other subsets of field generator coils. If the positionsensor 116 is determined to be in an overlapping working volume 114between adjacent working volumes, the EM system controller 108 maycontrol the switch module 110 to activate the subsets of field generatorcoils 104 corresponding to the adjacent working volumes 112.

During the sequential activation (for example, but not limited to,cycling) of the subsets of field generator coils 104, the local positionof the sensor 116 relative to the local coordinate system of the workingvolume 112 (for example, but not limited to, where the sensor 116 islocated) may be determined. The local position of the sensor 116 may bedetermined based on a distance between the sensor 116 and a referencepoint 101 in the local coordinate system. The reference point 101 maylie anywhere in the local coordinate system. For example, in someembodiments, the reference point 101 may be at an origin of the localcoordinate system. One or more subsets of field generator coils 104 maybe activated based on the distance between the sensor 116 and thereference point 101.

For example, when the reference point 101 is an origin of a localcoordinate system that is defined at a center of a control volume 112,and the position sensor 116 is located at or near the reference point101, only the subset of field generator coils corresponding to thatcontrol volume 112 may be activated. Conversely, when the positionsensor 116 is located far away from the reference point such that thesensor 116 is proximate to another control volume 112, adjacent subsetsof field generator coils 104 corresponding to both control volumes 112may be activated. It should be noted that the local coordinate systemneed not be defined at the center of a control volume 112. In some otherinstances, the local coordinate system may be defined near an edge orcorner of a control volume 112. Any placement of the reference point 101and/or the local coordinate system within a control volume 112 may becontemplated.

In some embodiments, the local position of the sensor 116 may bedetermined based on distances between the sensor 116 and a plurality ofreference points 101 in different local coordinate systems. Thedifferent local coordinate systems may lie in different control volumes112. The EM system controller 108 may be configured to determine aminimum distance from those distances, and activate a subset of fieldgenerator coils 104 corresponding to the control volume 112 based on theminimum distance.

During a surgical procedure, the EM system controller 108 may beconfigured to track the position and/or movement of the sensor 116within a control volume 112 corresponding to an active subset of fieldgenerator coils 104. As the position sensor 116 moves between adjacentcontrol volumes 112, different subsets of field generator coils 104 maybe selectively activated to ensure that the sensor 116 is continuouslytracked, while at the same time reducing EM field interference effects.

2. Closed-Loop Positional and Speed Feedback

FIG. 2 illustrates a block diagram of a closed-loop control EM trackingsurgical system, in accordance with some embodiments. As shown in FIG.2, a closed-loop control EM tracking surgical system 200 may comprise anEM system controller 108, a plurality of subsets of field generatorcoils 104-1 through 104-n, and a position sensor 116 operably connectedvia a feedback loop 107. Any number (n) of subsets of field generatorcoils 104 may be contemplated, and may depend in part on the strength ofeach subset of field generator coils 104 and/or a size (for example, butnot limited to, length and width) of a surgical bed (for example, butnot limited to, surgical bed 102 of FIG. 1).

In FIG. 2, a surgical tool may be automatically controlled using one ormore robotic arms that are in operable communication with the EM systemcontroller 108. The EM system controller 108 may be configured to trackand control the position and/or movement of the surgical tool, andselectively activate one or more subsets of field generator coils 104,based on positional and speed feedback of the position sensor 116 as thesensor 116 moves between different control volumes (for example, but notlimited to, control volumes 112 of FIG. 1).

As shown in FIG. 2, an input may be initially provided to the EMtracking surgical system 200. The input may comprise a desired positionand/or speed of a surgical tool. The position and/or speed of thesurgical tool may be controlled using the one or more robotic arms. TheEM system controller 108 may be configured to activate one or moresubsets of field generator coils 104, and to determine a control volume(for example, but not limited to, control volume 112) in which theposition sensor 116 is located. Once the control volume has beendetermined, the subset of field generator coils 104 corresponding tothat control volume may be activated while the other subsets of fieldgenerator coils 104 may be powered off. As previously described, theselective activation of different subsets of field generator coils 104can reduce EM field interference effects. The position and/or movementof the sensor 116 may be determined based on the interaction of thesensor 116 with the EM field within the control volume. The actualposition and/or speed of the surgical tool may be determined based onthe position and/or movement of the sensor 116, and may be comparedagainst the input to determine an amount of deviation Δ (if any) fromthe desired position and/or speed of the surgical tool. The EM systemcontroller 108 may be configured to adjust the actual position and/orspeed of the surgical tool (for example, but not limited to, via the oneor more robotic arms) based on the amount of deviation.

3. Switching Circuit

FIG. 3 illustrates a schematic circuit diagram of an EM trackingsurgical system, in accordance with some embodiments. As shown in FIG.3, an EM tracking surgical system 300 may comprise a plurality ofsubsets of field generator coils 104-1, 104-2, and 104-3 electricallyconnected to a power supply 118. An EM system controller 108 may be inoperable communication with a plurality of switches K1, K2, and K3 and aposition sensor 116. The plurality of switches K1, K2, and K3 may belocated in a switch module (for example, but not limited to, switchmodule 110 of FIG. 1). The EM system controller 108 may be configured toselectively activate one or more subsets of field generator coils 104,either simultaneously, sequentially, or in a round-robin configuration,based on a position and/or movement of the position sensor 116 withinand/or between adjacent control volumes (for example, but not limitedto, control volumes 112 of FIG. 1).

The EM system controller 108 may be configured to control one or moreswitches to selectively activate one or more subsets of field generatorcoils 104. For example, the EM system controller 108 may selectivelyactivate the first subset of field generator coils 104-1 by closing theswitch K1. Similarly, the EM system controller 108 may selectivelyactivate the second subset of field generator coils 104-2 by closing theswitch K2. Likewise, the EM system controller 108 may selectivelyactivate the third subset of field generator coils 104-3 by closing theswitch K3. In some embodiments, the EM system controller 108 maysimultaneously activate two or more subsets of field generator coils104. For example, the EM system controller 108 may simultaneouslyactivate the first and second subsets of field generator coils 104-1 and104-2 by closing the switches K1 and K2. Similarly, the EM systemcontroller 108 may simultaneously activate the first and third subsetsof field generator coils 104-1 and 104-3 by closing the switches K1 andK3. Likewise, the EM system controller 108 may simultaneously activatethe second and third subsets of field generator coils 104-2 and 104-3 byclosing the switches K2 and K3. Optionally, the EM system controller 108may simultaneously activate the first, second, and third subsets offield generator coils 104-1, 104-2, and/or 104-3 by simultaneouslyclosing the switches K1, K2, and/or K3, respectively. In someembodiments, the EM system controller 108 may sequentially close theswitches K1, K2, and/or K3. In some other embodiments, the EM systemcontroller 108 may close the switches K1, K2, and/or K3 in alternatingmanner. In some embodiments, the EM system controller 108 may close theswitches K1, K2, and/or K3 at a same frequency or at differentfrequencies. In some embodiments, the EM system controller 108 mayclose/open the switches K1, K2, and/or K3 for different lengths of time,so as to activate or power off the subsets of field generator coils 104for different lengths of time.

4. Layout of Field Generator Coils and Working Volumes

FIG. 4 illustrates schematic layouts of the field generator coils andworking volumes within an EM tracking surgical system, in accordancewith some embodiments. Part A of FIG. 4 illustrates a schematic sideview of a portion of an EM tracking surgical system 400, and Part B ofFIG. 4 illustrates a schematic top view of the portion of the system400.

As shown in FIG. 4, a first subset of field generator coils 104-1 and asecond subset of field generator coils 104-2 may be embedded along alength portion of a surgical bed 102. A first working volume 112-1 maybe defined above the first subset of field generator coils 104-1, and asecond working volume 112-2 may be defined above the second subset offield generator coils 104-2. The dimensions of the first working volume112-1 may be given by a length L1, a width W, and a height H. Thedimensions of the second working volume 112-2 may be given by a lengthL2, a width W, and a height H. In some embodiments, the lengths L1 andL2 may be substantially the same. In other embodiments, the lengths L1and L2 may be different. For example, in some instances, the length L1may be less than the length L2. In other instances, the length L1 may begreater than the length L2. In some alternative embodiments (not shown),the widths of the first and second working volumes 112 may be different.Optionally, the heights of the first and second working volumes 112 maybe different.

Each working volume 112 may comprise a sub-volume threshold locatedwithin each working volume. The sub-volume threshold is located at aboundary between overlapping working volumes. The sub-volume thresholdmay correspond to a transition zone as the sensor moves betweenoverlapping working volumes. For example, the first working volume 112-1may comprise a first sub-volume threshold 113-1, and the second workingvolume 112-2 may comprise a second sub-volume threshold 113-2. The firstsub-volume threshold 113-1 may have a length L1′, and the secondsub-volume threshold 113-2 may have a length L2′. In some embodiments,the lengths L1′ and L2′ may be substantially the same. In otherembodiments, the lengths L′ and L2′ may be different. The widths of thefirst and second sub-volume thresholds may be the same, and the heightsof the first and second sub-volume thresholds may be the same. In somealternative embodiments (not shown), the widths of the first and secondsub-volume thresholds may be different. Optionally, the heights of thefirst and second sub-volume thresholds may be different.

Each working volume 112 may further comprise a de-bounce thresholdlocated within each sub-volume threshold. For example, the first workingvolume 112-1 may comprise a first de-bounce threshold 115-1, and thesecond working volume 112-2 may comprise a second de-bounce threshold115-2. The second working volume may be activated once the sensor leavesthe first de-bounce threshold and enters the second de-bounce threshold.Similarly, the first working volume may be activated once the sensorleaves the second de-bounce threshold and enters the first de-bouncethreshold. Accordingly, the de-bounce thresholds may serve as“de-bouncing switches” for determining which working volume is to beactivated. The first de-bounce threshold 115-1 may have a length L1″,and the second de-bounce threshold 115-2 may have a length L2″. In someembodiments, the lengths L1″ and L2″ may be substantially the same. Inother embodiments, the lengths L1″ and L2″ may be different. The widthsof the first and second de-bounce thresholds may be the same, and theheights of the first and second de-bounce thresholds may be the same. Insome alternative embodiments (not shown), the widths of the first andsecond de-bounce thresholds may be different. Optionally, the heights ofthe first and second de-bounce thresholds may be different.

As shown in FIG. 4, the first and second working volumes may overlap soas to form a first overlapping working volume 114-1 disposed at aboundary between the first and second subsets of field generator coils104-1 and 104-2. The first and second working volumes 112-1 and 112-2may overlap by various amounts. For example, the first and secondworking volumes 112-1 and 112-2 may overlap by 1%, 2%, 5%, 10%, 15%,20%, 25%, 30%, or more than 30%. The first and second working volumes112-1 and 112-2 may be configured to overlap such that the positionsensor 116 can be accurately tracked and controlled near the boundariesof the control volumes 112, and as the position sensor 116 moves betweenadjacent working volumes 112. The first overlapping working volume 114-1may have a length U1, a width W, and a height H.

Each subset of field generator coils 104 may comprise a number of fieldgenerator coils 103. The number of field generator coils 103 in thesubsets may be same or different. As shown in part B of FIG. 4, eachsubset of field generator coils 104 may comprise eight field generatorcoils 103. The field generator coils 103 may be disposed along the edgesof the surgical bed 102 in two parallel rows 106. The field generatorcoils 103 may be spaced apart from one another along each row 106, at apitch p in the Y-direction. Laterally opposite field generator coils 103in the two rows 106 may be spaced apart by a distance d from each otherin the X-direction. The field generator coils 103 in the subsets 104 maybe spaced in a configuration that allows an EM field of a predeterminedstrength to substantially extend over each working volume 112.

5. Selective Activation of Field Generator Coils with One PositionSensor

FIG. 5 illustrates selective activation of field generator coils andworking volumes as a surgical tool comprising a position sensor thatmoves within an EM tracking surgical system, in accordance with someembodiments. Parts A, B, C, and D of FIG. 5 illustrate schematic topviews of a portion of an EM tracking surgical system 500.

As shown in part A of FIG. 5, a position sensor 116 may be disposed at adistal end of a surgical tool 117. The surgical tools may includeendoscopes, catheters, ureteroscopes, or other similar devices.Initially, the surgical tool 117 may be positioned such that theposition sensor 116 is located at position A. Position A may be a pointwithin a first working volume 112-1 above a first subset of fieldgenerator coils 104-1. An EM system controller (for example, but notlimited to, EM system controller 108) may detect that the positionsensor 116 is within the first working volume 112-1 and not in thesecond working volume 112-2. Additionally, the EM system controller maydetect that the position sensor 116 is within the first working volume112-1 but outside of a first overlapping working volume 114-1. The firstoverlapping working volume 114-1 may be an overlapping region betweenthe first and second working volumes 112-1 and 112-2. Accordingly, theEM system controller may selectively activate the first subset of fieldgenerator coils 104-1 without activating the second subset of fieldgenerator coils 104-2. When the first subset of field generator coils104-1 is activated, the first working volume 112-1 may become an activeworking volume, as indicated by the shaded region over the first workingvolume 112-1.

During a surgical procedure, the surgical tool 117 may move to adifferent location, such that the position sensor 116 may move toposition B shown in part B of FIG. 5. Position B may be a point thatlies within the first working volume 112-1 and the first overlappingworking volume 114-1. Since position B lies near the boundary of thefirst working volume 112-1, the EM system controller may activate thesecond subset of field generator coils 104-2 in addition to the firstsubset of field generator coils 104-1, to ensure that the positionsensor 116 can be accurately tracked near the boundary between adjacentworking volumes 112. When the first and second subset of field generatorcoils 104-1 and 104-2 are activated, the first and second workingvolumes 112-1 and 112-2 become active working volumes, as indicated bythe shaded regions over the first and second working volumes 112-1 and112-2.

Next, the surgical tool 117 may move to a different location, such thatthe position sensor 116 may move to position C shown in part C of FIG.5. Position C may be another point in the first overlapping workingvolume 114-1. However, unlike position B, position C may lie within thesecond working volume 112-2. Since position C lies near the boundary ofthe second working volume 112-2, the EM system controller may continueto activate both the first and second subsets 112, to ensure that theposition sensor 116 can be accurately tracked near the boundary betweenadjacent working volumes 112.

Next, the surgical tool 117 may move to a different location, such thatthe position sensor 116 may move to position D shown in part D of FIG.5. The EM system controller may detect that the position sensor 116 iswithin the second working volume 112-2 but outside of the firstoverlapping working volume 114-1. Accordingly, the EM system controllermay continue to activate the second subset of field generator coils104-2, but power off the first subset of field generator coils 104-1.

6. Selective Activation of Field Generator Coils with a Plurality ofPosition Sensors

FIG. 6 illustrates selective activation of field generator coils andworking volumes as a surgical tool comprising a plurality of positionsensors that move within an EM tracking surgical system, in accordancewith some embodiments. Parts A, B, and C of FIG. 6 illustrate schematictop views of a portion of an EM tracking surgical system 600. Theembodiment of FIG. 6 has similarities to the embodiment of FIG. 5.

In FIG. 6, a surgical tool 117 may be a flexible probe or shaft capableof twisting and bending about different directions. Additionally, thesurgical tool 117 may comprise a plurality of position sensors 116 thatinclude position sensors 116-1, 116-2, 116-3, 116-4, and 116-5. Forexample, a position sensor 116-1 may be disposed at a distal end of thesurgical tool 117, and a plurality of position sensors 116-2, 116-3,116-4, and 116-5 may be spaced apart along a length of the surgical tool117. By placing the plurality of position sensors 116 at differentlocations along the surgical tool 117, the position/orientation/shape ofthe surgical tool 117 can be determined through use of an EM field,which may be important during a surgical procedure as the tool 117 isbeing inserted into a patient's body. In some cases, theposition/orientation/shape of the surgical tool 117 that is obtained byan EM system controller can be mapped onto the fluoroscopic image of thepatient's body in real-time as the surgical procedure is beingperformed.

Additionally, in FIG. 6, more than two working volumes may be provided.For example, the EM tracking surgical system 600 may comprise threeworking volumes 112: a first working volume 112-1, a second workingvolume 112-2, and a third working volume 112-3. In examples, 4, 5, 6, 7,8, 9, 10, or more than 10 working volumes 112 may be provided.

As shown in part A of FIG. 6, the position sensors 116-1, 116-2, 116-3,116-4, and 116-5 may be located at positions A1, A2, A3, A4, and A5,respectively. Positions A1, A2, and A3 may lie within the first workingvolume 112-1 above a first subset of field generator coils 104-1.Positions A4 and A5 may lie outside of the first working volume 112-1and/or any working volume. An EM system controller (for example, but notlimited to, EM system controller 108 of FIG. 1) may detect that theposition sensors 116-1, 116-2, and 116-3 are within the first workingvolume 112-1, and not in the second and third working volumes 112-2 and112-3. Additionally, the EM system controller may detect that theposition sensors 116-1, 116-2, and 116-3 are within the first workingvolume 112-1 outside of a first overlapping working volume 114-1.Accordingly, the EM system controller may selectively activate the firstsubset of field generator coils 104-1 without activating the secondsubset of field generator coils 104-2.

During a surgical procedure, the surgical tool 117 may move from theposition shown in part A to the position shown in part B of FIG. 6.Referring to part B of FIG. 6, the position sensors 116-1, 116-2, 116-3,116-4, and 116-5 may be located at positions B1, B2, B3, B4, and B5,respectively. Position B1 may be a point that lies within the secondworking volume 112-2 outside of the first overlapping working volume114-1. Position B2 may be a point that lies within the second workingvolume 112-2 and the first overlapping working volume 114-1. Position B3may be a point that lies within the first working volume 112-1 and thefirst overlapping working volume 114-1. Positions B4 and B5 may bedifferent points that lie within the first working volume 112-1 outsideof the first overlapping working volume 114-1. Accordingly, the EMsystem controller may activate the second subset of field generatorcoils 104-2 in addition to the first subset of field generator coils104-1, to ensure that the position sensor 116 can be accurately trackedwithin the first and the second working volumes 112-1 and 112-2.

Next, the surgical tool 117 may move from the position shown in part Bto the position shown in part C of FIG. 6. Referring to part C of FIG.6, the position sensors 116-1, 116-2, 116-3, 116-4, and 116-5 may belocated at positions C1, C2, C3, C4, and C5, respectively. Positions C1and C2 may be different points that lie within the third working volume112-3 outside of a second overlapping working volume 114-2. Position C3may be a point that lies within the third working volume 112-3 and thesecond overlapping working volume 114-2. Positions C4 and C5 may bedifferent points that lie within the second working volume 112-2 outsideof the second overlapping working volume 114-2. None of the positionsC1-C5 lies within the first working volume 112-1 and/or the firstoverlapping working volume 114-1. Accordingly, the EM system controllermay activate the third subset of field generator coils 104-3 in additionto the second subset of field generator coils 104-2, to ensure that theposition sensor 116 can be accurately tracked within the second and thethird working volumes. Additionally, the EM system controller may poweroff the first subset of field generator coils 104-1 since none of theposition sensors 116 lies within the first working volume 112-1.

Although FIG. 7 illustrates the tracking of a surgical tool having aplurality of position sensors, one of ordinary skill in the art wouldappreciate that the EM system can also be used to track a plurality ofsurgical tools having a plurality of position sensors. Each surgicaltool may have one or multiple position sensors.

7. EM Tracking Surgical Systems Having Reconfigurable Bed Portions

FIG. 7 illustrates schematic views of an EM tracking surgical systemhaving reconfigurable bed portions, in accordance with some embodiments.Part A of FIG. 7 illustrates a side view of a portion of an EM trackingsurgical system 700 when a surgical bed is in a first position. Part Bof FIG. 7 illustrates the side view of the system 700 when the surgicalbed is in a second position.

As shown in FIG. 7, a surgical bed 102 may comprise reconfigurable bedportions that can move relative to each other. For example, the surgicalbed 102 may comprise a first bed portion 102-1 and a second bed portion102-2 connected at a hinge 124 that allows the bed portions to move (forexample, but not limited to, rotate and/or slide) relative to eachother. A first subset of field generator coils 104-1 may be embeddedalong a length of the first bed portion 102-1. A second subset of fieldgenerator coils 104-2 may be embedded along a length of the second bedportion 102-2. Accordingly, the first and second subsets of fieldgenerator coils 104 may be embedded along a length portion of thesurgical bed 102.

A first working volume 112-1 may be defined above the first subset offield generator coils 104-1, and a second working volume 112-2 may bedefined above the second subset of field generator coils 104-2, similarto the embodiment previously described in FIG. 4. In some embodiments,the dimensions and/or size of the first and second working volumes 112-1and 112-2 may be the same. Alternatively, the dimensions and/or size ofthe first and second working volumes 112-1 and 112-2 may be different.

As shown in FIG. 7, the first and second working volumes may overlap soas to form a first overlapping working volume 114-1 disposed at aboundary between the first and second subsets of field generator coils104-1 and 104-2. The first and second working volumes 112-1 and 112-2may be configured to overlap by various amounts. For example, the firstand second working volumes 112-1 and 112-2 may be configured to overlapby 1%, 2%, 5%, 10%, 15%, 20%, 25%, 30%, or more than 30%. The first andsecond working volumes 112-1 and 112-2 may be configured to overlap suchthat one or more position sensors, such as position sensors 116discussed above, can be accurately tracked and controlled near theboundaries of the control volumes 112, and as the position sensor(s) 116moves between adjacent working volumes 112.

Each subset of field generator coils 104 may comprise a number of fieldgenerator coils 103. The number of field generator coils 103 in thesubsets 104 may be same or different. In FIG. 7, each subset of fieldgenerator coils 104 may comprise eight field generator coils 103, forexample similar to the embodiment previously described in FIG. 4. Thefield generator coils 103 may be disposed along the edges of thesurgical bed 102 in two parallel rows (not shown in FIG. 7). The fieldgenerator coils 103 may be spaced apart from one another along each row(for example, but not limited to, at a pitch p in the Y-direction).Laterally opposite field generator coils 103 in the two rows may bespaced apart (for example, but not limited to, by a distance d) fromeach other in the X-direction. The field generator coils 103 in thesubsets 104 may be spaced in a configuration that allows an EM field ofa predetermined strength to substantially extend over each workingvolume 112.

As shown in FIG. 7, a global coordinate system 120 may be defined abovea center portion of the surgical bed 102. For example, the globalcoordinate system 120 may be defined above a boundary line between thefirst bed portion 102-1 and the second bed portion 102-2. An origin ofthe global coordinate system 120 may lie above the center portion of thesurgical bed 102 along the Z-direction. The origin of the globalcoordinate system 120 may also lie at a predetermined location above thehinge 124 when the surgical bed is in the position shown in part A ofFIG. 7. The origin of the global coordinate system 120 may serve as adatum point from which the positions of a patient's body, the subsets offield generator coils 104, and the working volume 112 may be defined.

A first local coordinate system 122-1 may be defined above a centerportion of the first bed portion 102-1. Likewise, a second localcoordinate system 122-2 may be defined above a center portion of thesecond bed portion 102-2. The first local coordinate system 122-1 may ormay not have an origin that lies at a center portion of the firstworking volume 112-1. Similarly, the second local coordinate system122-2 may or may not have an origin that lies at a center portion of thesecond working volume 112-2. For example, as shown in part A of FIG. 7,the origin of the first local coordinate system 122-1 may lie below thecenter portion of the first working volume 112-1, and in close proximityto the first bed portion 102-1. Likewise, the origin of the second localcoordinate system 122-2 may lie below the center portion of the secondworking volume 112-2, and in close proximity to the second bed portion102-2.

Vectors may be defined between the global coordinate system 120 and thelocal coordinate systems 122-1 and 122-2. For example, a vector T1 maybe defined from the origin of the first local coordinate system 122-1 tothe origin to the global coordinate system 120. A vector T2 may bedefined from the origin of the second local coordinate system 122-2 tothe origin to the global coordinate system 120. In some embodiments,another vector (not shown) may be defined from the origin of the firstlocal coordinate system 122-1 to the origin of the second localcoordinate system 122-2. The vectors T1 and T2 may be used to define thespatial relationship between the first working volume 112-1 and thesecond working volume 112-2. In particular, the vectors T1 and T2 may beused to define the spatial relationship between the first and secondworking volumes 112-1 and 112-2 relative to the datum point (forexample, but not limited to, origin of the global coordinate system 120)as the first and second bed portions 102-1 and 102-2 move relative toeach other.

As shown in part A of FIG. 7, the first bed portion 102-1 and the secondbed portion 102-2 may initially lie on a same horizontal plane extendingalong the Y-axis direction. The first and second bed portions 102-1 and102-2 may be configured to move relative to each other. For example, asshown in part B of FIG. 7, the first bed portion 102-1 may rotate by anangle θ in a clockwise direction about an X-axis extending through thehinge 124. The first bed portion 102-1 may be rotated, for example, tolower or raise a portion of a patient's body that is supported by thefirst bed portion 102-1. Since the first control volume 112-1 is definedby the EM field generated by the first subset of field generator coils104-1, the first control volume 112-1 may also rotate by the angle θ ina clockwise direction about the X-axis. As shown in part B of FIG. 7, itmay be observed that the origin of the first local coordinates system122-1 has shifted to a new location. Accordingly, a new vector T1′ maybe defined from the shifted origin of the first local coordinates system122-1 to the origin of the global coordinates system 120, whereby thevector T1′ is different from the vector T1. Since the second bed portion102-2 is not rotated relative to the global coordinates system 120, theorigin of the second local coordinates system 122-2 remains unchanged,and therefore the vector T2 remains the same. The vectors T1′ and T2 maybe used to define the spatial relationship between the first and secondworking volumes 112-1 and 112-2 relative to the datum point (forexample, but not limited to, origin of the global coordinate system 120)after the first bed portion 102-1 has moved relative to the second bedportion 102-2.

Although part B of FIG. 7B illustrates movement of the first bed portion102-1 relative to the second bed portion 102-2, the movement between thebed portions is not limited thereto. For example, in some embodiments,the second bed portion 102-2 may move relative to the first bed portion102-1. Optionally, the first and second bed portions 102-1 and 102-2 maysimultaneously move relative to each other such that the origins of thefirst and second local coordinate systems shift to different locations.The relative movement between the bed portions 102-1 and 102-2 maycomprise a rotational motion, a translational motion, and/or acombination of rotational and translational motion, about one or moreaxes. Accordingly, relative movement of the bed portions 102-1 and 102-2in one or more degrees of freedom (for example, but not limited to, sixdegrees of freedom) may be contemplated.

In some embodiments, a position, shape, and/or size of the overlappingworking volume 114 between adjacent working volumes may change when thebed portions move relative to each other. For example, as shown in partA of FIG. 7, a center (or centroid) of the first overlapping workingvolume 114-1 may be located at the origin of the global coordinatessystem 120. The first overlapping working volume 114-1 may have aregular shape (for example, but not limited to, defined by a length U1,width W, and height H, similar to the embodiment previously shown inFIG. 4).

When the first bed portion 102-1 rotates relative to the second bedportion 102-2, the position, shape, and/or size of the first overlappingworking volume 114-1 may change. For example, as shown in part B of FIG.7, the first overlapping working volume 114-1 may transform tooverlapping working volume 114-1′ having an irregular shape (forexample, but not limited to, having a trapezoidal-like profile as viewedfrom a side of the overlapping working volume 114-1′). The origin of theglobal coordinates system 120 remains unchanged by the relative rotationof the bed portions. Unlike part A of FIG. 7, the center (or centroid)of the overlapping working volume 114-1′ is not located at the origin ofthe global coordinates system 120 after the rotation. Instead, thecenter (or centroid) of the overlapping working volume 114-1′ may beoffset from the origin of the global coordinates system 120 by a vectorT3 after the rotation.

FIG. 8 illustrates a perspective view of an EM tracking surgical systemhaving a reconfigurable bed portion, in accordance with someembodiments. As shown in FIG. 8, an EM tracking surgical system 800 maycomprise a surgical bed 102 having a reconfigurable bed portion that ismovable move relative to a fixed bed portion. For example, the surgicalbed 102 may comprise a first bed portion 102-1 and a second bed portion102-2 that are disposed on a base 105. The base 105 may be supported bya stand 107. The first bed portion 102-1 may be operably connected to afirst portion of the base 105 via a hinge 124. The hinge 124 may bedisposed at a distal portion of the surgical bed 102 and/or the base105. The second bed portion 102-2 may be rigidly attached to a secondportion of the base 105. In some embodiments, the second bed portion102-2 may be integrally formed with the base 105. The hinge 124 mayallow movement (for example, but not limited to, rotational and/ortranslational) of the bed portions relative to each other. For example,the first bed portion 102-1 may be configured to rotate about the hinge124, such that the first bed portion 102-1 is rotatable relative to thesecond bed portion 102-2.

A plurality of field generator coils 103 may be embedded or integratedalong edge portions of the surgical bed 102. For example, as shown inFIG. 8, the plurality of field generator coils 103 may be embedded intwo parallel rows along a length of the first bed portion 102-1. Theplurality of field generator coils 103 may be positioned along the edgesof the first bed portion 102-1, so as to allow for unobstructed use offluoroscopy when a patient is placed on the first bed portion 102-1.Optionally, in some embodiments (not shown), a plurality of fieldgenerator coils may be further embedded along a length of the second bedportion 102-2 in two parallel rows.

The plurality of field generator coils 103 may include and can begrouped into subsets. For example, as shown in FIG. 8, the fieldgenerator coils 103 may include a first subset of field generator coils104-1 and a second subset of field generator coils 104-2. Although twosubsets are illustrated in FIG. 8, it should be noted that the inventionis not limited thereto, and that any number of subsets may becontemplated.

Each subset of field generator coils 104 may comprise a number of fieldgenerator coils 103. In the example of FIG. 8, each subset of fieldgenerator coils 104 may comprise four field generator coils 103.However, a subset of field generator coils need not be limited to fourfield generator coils. In some embodiments, a subset of field generatorcoils may comprise more than four field generator coils. In otherembodiments, a subset of field generator coils may comprise less thanfour field generator coils. Any number of field generator coils withineach subset may be contemplated.

FIGS. 9A and 9B illustrate sizing of a reconfigurable bed portion of anEM tracking surgical system based on exemplary dimensions of a humantorso, in accordance with some embodiments. FIG. 9A illustratesexemplary dimensions of a human torso and a working volume that isdefined based on those exemplary dimensions. FIG. 9B illustrates aschematic view of a patient who is placed on a reconfigurable bedportion of an EM tracking surgical system.

FIG. 9A illustrates exemplary dimensions of a human torso. For example,a length of a longest human torso (for example, but not limited to, asmeasured from neck to anus) may be about 32.9 inches, and a width of thehuman torso may be about 13 inches. A working volume of each subset offield generator coils may be defined based on those dimensions.

Referring to FIG. 9B, a patient may be placed on the first bed portion102-1 of the surgical bed 102 shown in FIG. 8. As shown in FIG. 9B, thefirst bed portion 102-1 may be rotated relative to the second bedportion 102-2, such that the patient's body is rotated an angle θrelative to a longitudinal axis Y1 extending longitudinally along thesecond bed portion 102-2.

A first working volume 112-1 and a second working volume 112-2 may beassociated with the first subset of field generator coils 104-1 and thesecond subset of field generator coils 104-2, respectively. In someembodiments, the first working volume 112-1 may be a cylinder. Thediameter of the cylinder may be about 5″, 6″, 7″, 8″, 9″, 10″, 11″, 12″,13″, 14″, 15″, 16″ 17″, 18″, 19″, 20″, 21″, 22″, 23″, 24″, 25″, orgreater than 25″. The height of the cylinder may be about 5″, 6″, 7″,8″, 9″, 10″, 11″, 12″, 13″, 14″, 15″, 16″ 17″, 18″, 19″, 20″, 21″, 22″,23″, 24″, 25″, or greater than 25″. In some examples, a cylinder mayhave a minimum diameter and height of about 5″×5″. In other examples, acylinder may have a maximum distance and height of about 25″×25″.Optionally, in some examples, each of the diameter and height of acylinder may be less than 5″, or greater than 25″. Optionally, the firstworking volume 112-1 may be a cuboid. The length of the cuboid may beabout 5″, 6″, 7″, 8″, 9″, 10″, 11″, 12″, 13″, 14″, 15″, 16″ 17″, 18″,19″, 20″, 21″, 22″, 23″, 24″, 25″, or greater than 25″. The width of thecuboid may be about 5″, 6″, 7″, 8″, 9″, 10″, 11″, 12″, 13″, 14″, 15″,16″ 17″, 18″, 19″, 20″, 21″, 22″, 23″, 24″, 25″, or greater than 25″.The height of the cuboid may be about 5″, 6″, 7″, 8″, 9″, 10″, 11″, 12″,13″, 14″, 15″, 16″ 17″, 18″, 19″, 20″, 21″, 22″, 23″, 24″, 25″, orgreater than 25″. In some examples, a cuboid may have a minimum length,width, and height of about 5″×5″×5″. In other examples, a cuboid mayhave a maximum length, width, and height of about 25″×25″×25″.Optionally, in some examples, each of the length, width, and height of acuboid may be less than 5″, or greater than 25″. The second workingvolume 112-2 may or may not have the same shape and/or dimensions as thefirst working volume 112-1. Any shape and/or dimensions for the firstand second working volumes may be contemplated.

As shown in FIG. 9B, a fluoroscopic imaging system 128 may be placedabove the patient's body. For example, the fluoroscopic imaging system128 may be placed within or above the second working volume 112-2. Thefluoroscopic imaging system 128 may be supported by a mechanical arm128-1 extending towards and/or over the first bed portion 102-1. In theexample of FIG. 9B, the fluoroscopic imaging system 128 may be used tocapture fluoroscopic images of the patient's body within the secondworking volume 112-2. Since the second subset of field generator coils104-2 is placed along the edges of the second bed portion 102-2, acentral portion of the surgical bed may be free enough of effects fromthe field generates such that fluoroscopy can be used with little or noobstruction.

FIG. 10 illustrates a reconfigurable bed portion of an EM trackingsurgical system, in accordance with some embodiments. As previouslydescribed in FIGS. 8, 9A, and 9B, a surgical bed 102 may comprise afirst bed portion 102-1 and a second bed portion 102-2 that may bedisposed on a base 105. The first bed portion 102-1 may be operablyconnected to a hinge 124 that allows the first bed portion 102-1 to move(for example, but not limited to, rotate and/or translate) relative tothe second bed portion 102-2.

As shown in FIG. 10, a first bed portion 102-1 may have a length L and awidth w. In some embodiments, the length L may be about 29.5 inches, andthe width w may be about 18.5 inches. In some embodiments, a cutout 130may be formed at an end of first bed portion 102-1, so as to preventmechanical interference as the first bed portion 102-1 moves relative tothe second bed portion 102-2. In the example of FIG. 10, the cutout 130may have a trapezoidal shape, and may be offset by a distances from anedge portion of the first bed portion 102-1.

The first bed portion 102-1 may further include two parallel rows 106 onits edges. As previously described, by placing a plurality of fieldgenerator coils along the two parallel rows 106 on the edges of thesurgical bed 102 (for example, but not limited to, the first bed portion102-1), unobstructed use of fluoroscopy can be achieved to image atleast a portion of a patient's body. Each row 106 may have a width oftthat is associated with an area of fluoro obstruction. In someembodiments, the width t may be less than or equal to about 2 inches. Itshould be noted that rows 106 constitute areas of fluoroscopyobstruction, since the field generator coils are radio-opaque.

FIG. 11 illustrates dimensions and locations of field generator coils ona reconfigurable bed portion of an EM tracking surgical system, inaccordance with some embodiments. In the example of FIG. 11, areconfigurable bed portion 102-1 of a surgical bed may have a length l′and a width w′. In some embodiments, the length l′ may be about 18.1inches, and the width w′ may be about 21.8 inches.

The bed portion 102-1 may further include two parallel rows 106 on itsedges. As previously described, by placing a plurality of fieldgenerator coils along two parallel rows on the edges of the surgicalbed, unobstructed use of fluoroscopy can be achieved to image at least aportion of a patient's body. Each row 106 may have a width of t′. Insome embodiments, the width t′ may be less than or equal to about 3.025inches. The two parallel rows 106 may be separated by a distance w1. Insome embodiments, the distance w1 may be about 15.75 inches.Additionally, rows 106 may constitute areas of fluoroscopy obstruction,since the field generator coils are radio-opaque.

As shown in FIG. 11, end portions 115 of the bed portion 102-1 maycorrespond to regions where adjacent working volumes overlap. The endportions 114 may be separated by a distance U2. In some embodiments, thedistance U2 may be about 14.5 inches.

FIG. 12 illustrates an estimated length of a working volume based on thedimensions of a reconfigurable bed portion of an EM tracking surgicalsystem, in accordance with some embodiments. As shown in FIG. 12, adistance from an edge of a hinge bearing 124 to an edge of a cutout 130of a first bed portion 102-1 may be denoted by l1. The distance l1 maybe indicative of a length of a total working volume above the first bedportion 102-1. In some embodiments, the distance l1 may be about 26.5inches. FIG. 12 also illustrates first bed portion 102-1 angled withrespect to second bed portion 102-2.

FIG. 13 illustrates an exemplary working volume above a reconfigurablebed portion of an EM tracking surgical system, in accordance with someembodiments. As shown in FIG. 13, a total working volume 112 may bedefined above a first bed portion 102-1 of a surgical bed 102. In FIG.13, first bed portion 102-1 is shown angled with respect to second bedportion 102-2. The total working volume 112 may comprise a first workingvolume 112-1 and a second working volume 112-2. The total working volume112 may have a length L_(T), a width W, and a height H. In someembodiments, the length LT may be about 31 inches, the width W may beabout 19 inches, and the height H may be about 19.7 inches. It should benoted that the invention is not limited thereto, and that any dimensionsof the total working volume may be contemplated. As previouslydescribed, the first working volume 112-1 and the second working volume112-2 may overlap, which can help to minimize deadzones (for example,but not limited to, places where a position sensor cannot be tracked,either due to a weak EM field or EM interference).

As used herein A and/or B encompasses one or more of A or B, andcombinations thereof such as A and B. It will be understood thatalthough the terms “first,” “second,” “third” etc. may be used herein todescribe various elements, components, regions and/or sections, theseelements, components, regions and/or sections should not be limited bythese terms. These terms are merely used to distinguish one element,component, region or section from another element, component, region orsection. Thus, a first element, component, region or section discussedbelow could be termed a second element, component, region or sectionwithout departing from the teachings of the present invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including,” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components and/or groupsthereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top” may be used herein to describe one element's relationship to otherelements as illustrated in the figures. It will be understood thatrelative terms are intended to encompass different orientations of theelements in addition to the orientation depicted in the figures. Forexample, if the element in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on the “upper” side of the other elements. The exemplary term“lower” can, therefore, encompass both an orientation of “lower” and“upper,” depending upon the particular orientation of the figure.Similarly, if the element in one of the figures were turned over,elements described as “below” or “beneath” other elements would then beoriented “above” the other elements. The exemplary terms “below” or“beneath” can, therefore, encompass both an orientation of above andbelow.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. Numerous differentcombinations of embodiments described herein are possible, and suchcombinations are considered part of the present disclosure. In addition,all features discussed in connection with any one embodiment herein canbe readily adapted for use in other embodiments herein. It is intendedthat the following claims define the scope of the invention and thatmethods and structures within the scope of these claims and theirequivalents be covered thereby.

What is claimed is:
 1. An electromagnetic (EM) system for tracking asurgical tool, comprising: a plurality of subsets of field generatorcoils disposed along edge portions of a surgical bed, wherein eachsubset of field generator coils is configured to generate a magneticfield within a corresponding control volume, wherein a first controlvolume generated by a first subset at least partially overlaps a secondcontrol volume generated by a second subset; a position sensor disposedon a portion of the surgical tool, wherein the position sensor isconfigured to generate a sensor signal in response to one of themagnetic fields when the position sensor is located inside acorresponding one of the control volumes; and an EM system controllerconfigured to: activate the first control volume and deactivate thesecond control volume in response to determining that the positionsensor is located in the first control volume but outside of anoverlapping portion of the first and second control volumes, determine aspeed and a direction of movement of the surgical tool based on thesensor signal, and activate the first and second control volumessimultaneously based on the speed and the direction of movement of thesurgical tool, in response to determining that the position sensor islocated in the overlapping portion.
 2. The system of claim 1, whereinthe subsets of field generator coils are integrated longitudinally alongthe edge portions of the surgical bed.
 3. The system of claim 1, whereineach control volume is defined by a space proximate to the respectivesubset of field generator coils.
 4. The system of claim 1, wherein theEM system controller is configured to track the surgical tool based onthe sensor signal.
 5. The system of claim 4, wherein the EM systemcontroller is configured to track the surgical tool by selectivelyactivating one or more of the subsets of field generator coils dependingon the sensor signal.
 6. The system of claim 1, wherein the EM systemcontroller is configured to deactivate the first subset of fieldgenerator coils and activate the second subset of field generator coilswhen the position sensor moves from the first control volume to thesecond control volume.
 7. The system of claim 1, wherein each controlvolume comprises a local coordinate frame having a reference point. 8.The system of claim 7, wherein the sensor signal is indicative of adistance between the position sensor and the reference point.
 9. Thesystem of claim 8, wherein the one or more subsets of field generatorcoils are activated based on the distance between the position sensorand the reference point.
 10. The system of claim 1, wherein a centralportion of the surgical bed is fluoroscopically transparent.
 11. Thesystem of claim 1, wherein a portion of the field generator coils aremovable with respect to the surgical bed.
 12. The system of claim 1,wherein an amount of overlap between the first and second controlvolumes is selected to provide continuous tracking of the surgical tool.13. An electromagnetic (EM) system for tracking a surgical tool,comprising: a plurality of subsets of field generator coils disposedalong edge portions of a surgical bed, wherein each subset of fieldgenerator coils is configured to generate a magnetic field within acorresponding control volume; a position sensor disposed on a portion ofthe surgical tool, wherein the position sensor is configured to generatea sensor signal in response to one of the magnetic fields when theposition sensor is located inside a corresponding one of the controlvolumes; and an EM system controller configured to: determine a speed ofthe surgical tool based on the sensor signal, determine a direction ofmovement of the surgical tool based on the sensor signal, and activateone or more of the subsets of field generator coils based on the speedand the direction of movement of the surgical tool.
 14. The system ofclaim 13, wherein the EM system is further configured to: determine adesired speed of the surgical tool, and determine a deviation of thespeed of the surgical tool from the desired speed of the surgical tool.15. The system of claim 14, wherein the EM system is further configuredto: adjust the speed of the surgical tool based on the deviation. 16.The system of claim 13, wherein a first control volume generated by afirst subset at least partially overlaps a second control volumegenerated by a second subset and wherein the EM system is furtherconfigured to: activate the first control volume and deactivate thesecond control volume in response to determining that the positionsensor is located in the first control volume but outside of anoverlapping portion of the first and second control volumes, andactivate the first and second control volumes simultaneously in responseto determining that the position sensor is located in the overlappingportion.
 17. An electromagnetic (EM) system for tracking a surgicaltool, comprising: a plurality of subsets of field generator coilsdisposed along edge portions of a surgical bed, wherein each subset offield generator coils is configured to generate a magnetic field withina corresponding control volume; a position sensor disposed on a portionof the surgical tool, wherein the position sensor is configured togenerate a sensor signal in response to one of the magnetic fields whenthe position sensor is located inside a corresponding one of the controlvolumes; and an EM system controller configured to: sequentiallyactivate the subsets of field generator coils in response to receivingan initialization input, determine which of the control volumes in whichthe position sensor is located based on the sensor signal, determine aspeed and a direction of movement of the surgical tool based on thesensor signal, and activate the control volume in which the positionsensor is located and deactivate other control volumes based on thecontrol volume in which the position sensor is located, the speed andthe direction of movement.
 18. The system of claim 17, wherein the EMsystem is further configured to: determine whether the position sensoris located in any of the control volumes, wherein determining which ofthe control volumes in which the position sensor is located is performedin response to determining that the position sensor is located in any ofthe control volumes.
 19. The system of claim 17, wherein each controlvolume comprises a local coordinate frame having a reference point andwherein the sensor signal is indicative of a distance between theposition sensor and the reference point.
 20. The system of claim 19,wherein the EM system is further configured to: selectively activate thesubsets of field generator coils based on the distance between theposition sensor and the reference point.
 21. The system of claim 17,wherein a first control volume generated by a first subset at leastpartially overlaps a second control volume generated by a second subsetand wherein the EM system is further configured to: activate the firstcontrol volume and deactivate the second control volume in response todetermining that the position sensor is located in the first controlvolume but outside of an overlapping portion of the first and secondcontrol volumes, and activate the first and second control volumessimultaneously in response to determining that the position sensor islocated in the overlapping portion.
 22. The system of claim 17, whereina portion of the field generator coils are movable with respect to thesurgical bed.
 23. An electromagnetic (EM) system for tracking a surgicaltool, comprising: a plurality of subsets of field generator coilsdisposed along a surgical bed, wherein each subset of field generatorcoils is configured to generate a magnetic field within a correspondingcontrol volume, wherein a first subset of the field generator coils isconfigured to generate a first control volume and a second subset of thefield generator coils is configured to generate a second control volumethat at least partially overlaps the first control volume; and an EMsystem controller configured to: receive a sensor signal from a positionsensor disposed on the surgical tool, the sensor signal indicative of aposition of the surgical tool, determine which of the control volumesthe surgical tool is located in based on the sensor signal, deactivatethe second control volume based on determining that the position sensoris located in the first control volume but outside of an overlappingportion of the first and second control volumes, determine a speed anddirection of movement of the surgical tool based on the sensor signal,and activate the first and second control volumes simultaneously basedon the speed and direction of movement of the surgical tool, in responseto determining that the position sensor is located in the overlappingportion.
 24. The system of claim 23, wherein the EM system is furtherconfigured to: determine whether the surgical tool is located in any ofthe control volumes, wherein determining which of the control volumes inwhich the surgical tool is located is performed in response todetermining that the position sensor is located in any of the controlvolumes.
 25. The system of claim 23, wherein the surgical tool isconfigured to house a position sensor at a distal end of the surgicaltool.
 26. The system of claim 25, wherein the position sensor isconfigured to generate the sensor signal.
 27. The system of claim 23,wherein each control volume comprises a local coordinate frame having areference point and wherein the sensor signal is indicative of adistance between the surgical tool and the reference point.